In order to be competitive in the market and to serve customers better, modern photographic films based on silver halide emulsions need to be manufactured with the highest quality and the lowest cost possible. Robust or reliably reproducible emulsion manufacturing becomes very important in order to meet such requirements.
Spectral sensitizing dyes are usually manufactured as a salt with a counter ion. The counter ion is usually chosen for ease of manufacturing. Photoefficiency of spectral sensitizing dyes is not usually determined by the counter ion. However, in recent tabular grain spectral sensitization experiments, Dye 1 with triethylamine ion as counter ion unexpectedly showed a lack of finish reproducibility and often required much higher temperatures to reach the maximum speed (sensitivity) than Dye 2 with N-ethylpyridinium ion as counter ion.
L. E. Oppenheimer, A. H. Herz, and T. H. James reported that N-alkyl pyridinium or quinolinium ions and their chain substituted analogs promoted growth of Lippmann-type silver bromide grains; (Oppenheimer, James, Herz in particle Growth in Suspensions, A. L. Smith ed., Academic Press, London, 1973, p.159). Adsorption properties of such cationic surfactants are reported by J. F. Padday and A. H. Herz in Chaper 1 of the 4th Edition of The Theory of the Photographic Process, T. H. James ed., Macmillan, 1977, p. 25.
A recent European Patent Application 0 472 004A of Dobles et al disclosed supersensitizer combinations of low staining dyes such as Dye 1 and Dye 2.